1. Field of the Invention
The invention relates to a digitizing stylus having a contacting pin of ferromagnetic material. Such contacting pins can be moved into the shaft of the stylus against a spring force, this movement being limited in the axial direction, and with an inner end region oriented toward the shaft, it extends into or through the center opening of a toroid coil, and is coupled with a switching device. As the contacting pin moves into the shaft, this switching device closes a circuit of exciter current for the toroid coil.
2. Brief Description of the Prior Art
Digitizing styli of this kind are used in order to perform a digital storage of illustrations with the aid of so-called digitizing tablets which have a fine-meshed wire grid. The contacting pin of the digitizing stylus is pressed against a point of a drawing located on the digitizing tablet to be stored in memory, causing the displacement of the contacting pin into the shaft of the digitizing stylus, which in turn causes the contacting pin to generate a switching signal. As a consequence of the switching signal, a magnetic field is generated in order to fix a point on the surface of the digitizing tablet, the field originating with either the coil or the wire grid of the digitizing tablet. In the first instance, the toroid coil acts as a transmitter; in the second, it acts as a receiver. If the toroid coil is considered to be the transmitter coil, then with an exciter current flowing through the coil a magnetic field is generated which is carried by the ferromagnetic contacting pin in such a way that at the corresponding point of the wire grid of the digitizing tablet, a pulse is inductively generated, the position of which is fixed with respect to the wire grid and stored in memory.
In known digitizing styli of this type, when the contacting pin is pressed into the shaft of the digitizing stylus it moves into the center opening of the toroid coil, so that the intensity of the magnetic field transmitted by the contacting pin depends upon how far the contacting pin has been moved into the center opening upon the actuation of the switching device, or in other words, upon the excitation of the toroid coil. However, the contacting pin conventionally continues to move still farther into the center opening of the toroid coil after the actuation of the switching device before being arrested by a mechanical stop. Therefore, in known digitizing styli, an induction is generated for the wire grid which has a certain value upon the actuation of the switching device, but then increases as the displacement of the contacting pin continues. The result is a pulse in the wire grid, which deviates substantially from the rectangular form.